Powder processing of FeAl sheets by roll compaction

Powder metallurgical processing techniques were employed to manufacture 0.2 mm thickness of iron aluminide sheets based on Fe-40 at% Al using water atomized powder of an FeAl alloy containing C, B, Mo and Zr as alloying elements. Powders of FeAl mixed with polymeric binders were roll compacted using two counter rotating rolls to a thickness of approximately 0.66 mm. Roll compacted sheets were then debindered in nitrogen using a two stage debindering cycle over a period of several hours to effectively decompose the binder. Debindered sheets were vacuum sintered prior to cold rolling them for densification in several different stages. The properties of the FeAl sheets are dependent on the processing temperature, Al content of the final sheet, oxygen content, and the microstructure. Sheets exhibit fine microstructure with a dispersion of Al₂O₃ particles throughout the matrix. Variation of electrical resistivity, specific heat, thermal expansion, and thermal diffusivity with variation of temperature is presented, and compared with 304 steel.     

Development of powder metallurgy T42 high speed steel for structural applications

Water atomized T42 high speed steel powders have been processed by a powder metallurgy (PM) route in order to obtain a fully dense material suitable for valve seat inserts (VSI) in diesel engines. Two different heat treatments (isothermal annealing and multitempering) were designed leading to the targeted hardness value (50 HRC). Microstructural characterisation of the heat-treated material was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fracture strength and fracture toughness have also been investigated. The wear behaviour was evaluated through pin-on-disc tests at service temperature (360 °C). The obtained results demonstrated the excellent wear resistance of the VSI material without severe wear of the countermaterial (valve).     

热喷涂FeAl涂层中纳米晶结构的XRD分析

利用超音速火焰喷涂（HVOF）和大气等离子喷涂（APS）工艺分别喷涂了雾化（微米结构的）以及球磨（纳米结构的）Fle-Al粉末制备了不同结构的涂层．两种原料粉末和喷涂工艺均引起涂层的XRD峰异常宽化．由宽化峰给出的晶粒尺寸与TEM测出的晶粒尺寸有较大的差异．结合SEM、电子探针以及TEM的测试结果，同时考虑到涂层中形成的结构缺陷以及化学成分的不均匀性，证实异常宽化来自喷涂过程中由于Al的耗损导致的FeAl相中Al的成分不均匀分布．     

纯铝中间层厚度对铝/钢点焊接头性能的影响

采用纯铝作为中间层对铝合金与低碳钢进行了电阻点焊,分析中间夹层厚度对界面反应层厚度和接头抗拉强度的影响。在钢/中间夹层界面观察到有界面反应层生成,其主要由靠近钢侧的Fe2Al5和靠近中间夹层铝侧的FeAl3两种金属间化合物组成。与不加中间夹层相比,利用纯铝作为中间夹层点焊的铝合金与低碳钢的接头具有较薄的界面反应层和较高的接合强度。随着中间夹层厚度的增加,界面反应层厚度逐渐减小,而接头抗拉强度则呈增大趋势。结果表明,采用纯铝作为中间夹层点焊铝合金与钢具有一定的有效性。     

A Novel,Amorphous, Non-equiatomic FeCrAlCuNiSi High-Entropy Alloy with Exceptional Corrosion Resistance and Mechanical Properties

The exceptional corrosion resistance and mechanical properties of high-entropy metallic glasses(HE-MGs) are highly desirable for diverse critical applications.However,a long-standing problem of these alloys is that their alloy design approaches are based on limited equiatomic or near-equiatomic ratios.In this study,a novel senary alloy(non-equiatomic Fe_3 Cr_2 Al_2 CuNi_4 Si_5) with amorphous structure was prepared.This alloy exhibited exceptional corrosion resistance and Vickers hardness as high as～1 150 Hv at room temperature.The processing route involved amorphous powder molding via a mechanical alloying and ultrahigh pressure consolidation technique,resulting in an optimal microstructure of amorphous structure with nanoparticles uniformly distributed in the matrix alloy.This approach can effectively inhibit the crystallization of amorphous structure,thus providing a general pathway for manufacturing next-generation non-equiatomic HE-MGs with both exceptional corrosion resistance and strength.     

大气等离子喷涂球磨Fe-Al合金制备FeAl涂层及其结构表征

FeAl金属间化合物具有良好的抗高温氧化和硫化、抗高温冲蚀性能与较高的高温强度,且密度小、成本低。将FeAl用作SOFC支撑体材料,不仅可提高SOFC的高温强度,而且可显著降低其制作成本。本研究采用机械合金化工艺制备了Fe–35Al粉末,通过大气等离子喷涂(APS)制备了FeAl涂层。利用XRD、SEM表征了球磨粉末及热处理前后涂层的微观结构。研究结果表明,通过大气等离子喷涂球磨粉末,可以制备出FeAl金属间化合物涂层,涂层经800℃热处理30h后,可提高FeAl相的有序度。     

FeAl基合金的高温抗氧化性能分析

设计了二组化学成分不同的FeAl基合金,进行了1000℃的高温氧化试验,并对其进行了分析.结果表明,含碳量较高的材质较普通FeAl基合金的硬度高;B元素改善品界脆性,Zr使晶界同溶强化,提高了材料的冲击韧度和抗托强度;1000℃下,含碳量较低的FeAl基合金呈完全抗氧化性,其循环氧化动力学曲线均服从抛物线规律.     

Temperature induced porosity in hot isostatically pressed gamma titanium aluminide alloy powders

In this study the occurrence of temperature induced porosity (TIP) in hot isostatically pressed (HIP) compacts of different gamma Titanium aluminide alloys was investigated. Two gamma Titanium aluminide alloys Ti-48.9at.%Al and an advanced Niobium containing alloy Ti-46at.%Al-9at.%Nb have been atomized by gas atomization and by centrifugal atomization in an inert gas atmosphere. The alloy powders were studied regarding porosity and the content of inert gas entrapped in the powder particles. Selected powder batches were hot isostatically pressed at 1280 °C and were investigated with respect to TIP evolution after a high temperature exposure to 1390 °C for short and long time periods. It was found that gas atomized Titanium aluminide alloy powders contain a certain amount of atomization gas, the concentration of which increases with the powder particle size. The amount of inert gas entrapped in centrifugally atomized powders is higher as compared to powders produced by gas atomization. The occurrence of TIP after high temperature annealing of the HIP’ ed compacts depends on the grain size, the processing medium (Argon or Helium), the amount of entrapped inert gas and the annealing time. Guidelines are presented for minimizing or prevention of TIP in γ-TiAl alloys processed by powder metallurgy.     

增材制造用高流动性铝合金粉末制备技术研究

采用自主开发的旋转盘离心雾化实验装置进行雾化制备增材制造用铝合金粉末实验研究,通过开展雾化盘实验研究优选出粒度分布较均匀收得率较好的盘形,并获得其结构和工艺参数的影响规律;通过对制得的铝合金粉末性能和3D打印成型件物理性能进行检测。结果表明:离心雾化制备的铝合金粉末具有高流动性、窄粒度、高球形度、高松比,表面光洁无卫星粉,无空心粉等特点,同时3D打印离心雾化样件熔覆道均匀,孔洞缺陷少,致密度和力学性能明显优于气雾化样件,尤其是抗拉强度和屈服强达到495和320 MPa,相比气雾化粉打印样件提高近10%。     

Studies of Fe-40Al coatings obtained by high velocity oxy-fuel

Interesting properties that intermetallics possess have made them to be promising materials to be used either as bulk materials or as coatings, both at medium or elevated temperature environments. This group of materials possesses a long-range order, which can be kept by some intermetallics until their melting point, which is the main reason why they possess a good stability at high temperatures. Some other properties can be summarized as follows: high thermal conductivity; low density; great strength, particularly at high temperatures; good oxidation resistance at high temperatures (because of the formation of oxide films); low ductility, brittle fracture at room temperature.FeAl coatings from powder of nominal composition Fe-40Al-0.05 Zr (at.%) with 50 ppm B and 1 wt.% Y₂O₃ have been prepared using high velocity oxy-fuel (HVOF) technique. Several standard spraying conditions have been assessed; some parameter variations from those standards intend to find optimal spraying conditions. The characterization has been carried out by DRX, EDS and Scanning Electron Microscopy. The results conclude that a major intermetallic FeAl phase has been obtained.Microhardness and wear properties have been evaluated for those coatings obtained with optimal conditions. Compared to room temperature sliding wear behaviour, the friction coefficient is reduced when the test is performed at 400 °C.     

Improvement of product strength and formability in stamping of Al–Mg–Si alloy sheets having bake hardenability by resistance heat and artificial aging treatments

Resistance heat and artificial aging treatments were introduced into a stamping operation to improve the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability used for automobile body panels. In this treatment, the sheets undergo re-solution by resistance heat treatment, composed of resistance heating and water quenching just before the stamping. Stamped sheets are artificially aged just after the stamping to increase product strength. In the experiment, Al–0.60% Si–0.74% Mg alloy sheets were chosen as an example of Al–Mg–Si alloy sheets having bake hardenability. The re-solution solution treatment of the sheets was sufficiently accomplished by rapid resistance heat treatment, and formability of the sheets was improved. Hardness of the formed products was increased by artificial aging. It was found that the present process is effective in improving the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability due to the compactness and rapidness.     

Self-piercing riveting of high tensile strength steel and aluminium alloy sheets using conventional rivet and die

High tensile strength steel sheets having different strengths were joined with an aluminium alloy sheet by a self-piercing rivet. In the joining, a conventional rivet and die used for aluminium alloy sheets were employed in order to have the versatility for various steel sheets. The effects of the flow stress of the high strength steel sheets and the combination of the sheets on the joinability of the sheets were investigated by finite element simulation and an experiment. As the tensile strength of the high strength steel sheet increases, the interlock for the upper high strength steel sheet increases due to the increase in flaring during the driving through the upper sheet, whereas that for the lower high strength steel sheet decreases. The joint strength for the lower high strength steel is comparatively smaller than that for the upper high strength steel sheet. It was found that the high tensile strength steel sheets below 590 MPa were fully joined with the aluminium alloy sheet even with the conventional self-piercing rivet and die.     

Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

FeAl intermetallic compound coating was prepared by cold spraying using a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950 °C. The high-temperature abrasive wear test was carried out for the FeAl coating at a temperature range from room temperature to 800 °C. The high-temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 to 800 °C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800 °C by a factor of 3.     

热补偿电阻点焊镁合金接头的性能

采用热补偿电阻点焊方法进行焊接镁合金板试验,并分析了焊接电流、焊接时间及电极压力等焊接参数对生成熔核的尺度与接头抗剪强度的影响。试验结果表明,采用热补偿电阻点焊方法焊接镁合金,能在较低的焊接电流条件下获得具有较大熔核及较高抗剪强度的点焊接头。因而,采用热补偿电阻点焊方法焊接镁合金是有效的。     

LAVES PHASE ALLOYS FOR HIGH TEMPERATURE APPLICATIONS

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Effect of chromium on the mechanical properties of powder-processed Fe–0.45 wt.% P alloys

The present investigation shows the role of chromium in Fe–P binary and Fe–P–Cr ternary alloys. The compositions are characterized in terms of microstructure, porosity content, hardness and tensile properties. The alloys were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs. Then the slabs were hot rolled and annealed to relieve the residual stresses. Densifications as high as 98.9% of theoretical density have been realized. Microstructures of these alloys consist of single-phase ferrite only. Both Fe–0.45P and Fe–0.45P–3Cr alloys showed very high strength. As forged and hot rolled Fe–0.45P alloy showed low elongation. It was observed that, the addition of Cr to Fe–P based alloys caused an increase in strength associated with the reduction in ductility. Alloys developed in the present investigation were capable of hot working to very thin gage of sheets and wires.     

Enhanced corrosion resistance of high strength Mg–3Al–1Zn alloy sheets with ultrafine grains in a phosphate-buffered saline solution

The corrosion behaviour of ultrafine grained AZ31Mg alloy sheets with very high strength, which were prepared by high-ratio differential speed rolling (HRDSR) technique, was studied in a phosphate-buffered saline solution. The corrosion resistance was greatly improved after HRDSR. This result was attributed to the enhanced stability of the Mg(OH)₂ layer due to the grain refinement and precipitation of various types of P-containing compounds on the stabilised Mg(OH)₂ layer. The HRDSR technique has a good potential to be used for the development of magnesium sheets with good combination of mechanical and biocorrosion properties.     

TiO2粉末介质介入铝合金电阻点焊熔核形核电阻特征分析

以TiO2粉末作为添加介质进行铝合金电阻点焊. 焊接过程中利用实时传感技术对电阻点焊熔核形核过程的电极电压与焊接电流信号进行实时检测,通过对检测信号的计算和分析得到熔核形核动态电阻曲线,研究TiO2粉末介质对熔核形核与生长过程电阻特征的影响. 结果表明,随着TiO2粉末介质的介入,熔核形核动态过程发生变化,表现出不同的动态电阻特征. 由动态电阻曲线提取的接触电阻、终了电阻和形核电阻热效应3个特征值均能反映TiO2粉末介质对熔核形核质量特征的影响,且终了电阻、形核电阻热与焊点最大承载力高度线性相关,可作为检测熔核形核质量的依据.     

Moisture and hydrogen-induced embrittlement of iron aluminides

It is now apparent that Fe₃Al and FeAl alloys with less than 40 at.% Al are intrinsically ductile. Brittleness is manifested only in environments providing ready access to hydrogen. Microstructure, alloy content and surface condition may alter somewhat the susceptibility to embrittlement by moisture or by hydrogen, but are key considerations in alloy design for toughness or ductility when aluminum content is within the Fe₃Al-FeAl range. The susceptibility of iron aluminides to moisture and to hydrogen is a major factor hampering their development as structural alloys. Other properties which need to be improved include tensile strength and creep and impact resistance, but approaches to achieve improved strength properties must consider the susceptibility to the external environment. Development of alloys with less than 16% Al appears to be attractive for situations where reduced strength and oxidation resistance can be tolerated because of the insensitivity of these alloys to embrittlement. However, it must be realized that these alloys are not intermetallics.     

Influence of Welding Parameters on the Tensile Shear Strength of Aluminum Alloy Joint Welded by Resistance Spot Welding

Aluminum alloy A5052 sheets were welded using the technique of resistance spot welding with cover plates. The effects of welding parameters on the tensile shear strength of the joints were investigated. The results reveal that the technique is feasible to weld aluminum alloy, and that the enhanced electrode force is more effective than the extended down-sloping time for inhibiting pores formation and increasing the strength of the joint.